The following abbreviations are herewith defined:
3GPP third generation partnership project
AT allocation table (PDCCH)
CQI channel quality indicator/indication
DL downlink
DRX/DTX discontinuous reception/discontinuous transmission
eNB evolved nodeB (of an LTE system)
E-UTRAN evolved UTRAN (LTE or 3.9G)
LTE long term evolution of 3GPP
MAC medium access control
MCS modulation and coding scheme
Node B base station or similar network access node
PDCCH physical downlink control channel
PRB physical resource block
PS packet scheduler
PUCCH physical uplink control channel
RRC radio resource control
TTI transmission time interval
UE user equipment (e.g., mobile equipment/station)
UL uplink
UMTS universal mobile telecommunications system
UTRAN UMTS terrestrial radio access network
VoIP voice over IP (internet protocol)
A proposed communication system known as evolved UTRAN (E-UTRAN, also referred to as UTRAN-LTE, E-UTRA or 3.9G) is currently under development within the 3GPP. One specification of interest to these and other issues related to the invention is 3GPP TS 36.213, V8.2.0 (2008-03), 3rd Generation Partnership Project; Technical Specification Group Radio Access Network; Evolved Universal Terrestrial Radio Access (E-UTRA); Physical layer procedures (Release 8), which is attached to the priority document as Exhibit A.
Relevant to this invention is the concept of resource allocations on a common channel over which multiple users receive resources specifically allocated to only one of them. LTE is one such system that employs this concept. In LTE, the network assigns resources to UE's using the physical downlink control channel (PDCCH, also referred to as allocation table AT). The network schedules UE's at certain points in time which are clearly defined and synchronized between the network and the various UEs being allocated. These instants in time are also referred to as DRX timeout periods (from the UE point of view). This allows the UE to re-tune its receiver from its downlink data channel to the PDCCH in a manner in which it will not miss transmissions scheduled for it on either channel, and to conserve its battery power by operating in a reduced power state (except for scheduled paging instances) when not scheduled to receive. A similar scheduling option exists on the UE's transmit side, termed a DTX period.
At each DRX the UE will read one or more PDCCH (this specific amount is also ‘negotiated’ or otherwise commanded by the network previously, e.g. during setup of a connection with the UE) in which the UE may then be assigned UL and/or DL resources by the network.
This flexibility for scheduling resources leads to the potential for two problems, most pronounced when there is a large number of active users all generating a large amount of small data packages with tight delay constraints (e.g. VoIP, gaming etc.). This dynamic scheduling can then lead to large control signaling overhead compared to the actual transferred data, or to the wasting of air interface resources due to lack of addressing possibilities (not enough space in AT/PDCCH for addressing a sufficient number of UEs to allocate all available resources).
The LTE system and others address those problems with the concept of persistent scheduling, where a resource allocated to a particular UE remains a valid allocation for more than the next TTI. This means that the UL or DL resources are allocated in a persistent manner, i.e. the resource allocation is given by the network only in the beginning of the data transmission, not for each data packet separately. In semi persistent allocation only the first transmissions use the persistent allocation while retransmissions are explicitly scheduled. The agreement in 3GPP radio access network working group 2 (RAN WG2) is to allocate the resources for persistent transmissions using PDCCH signalling.
With persistent/semi-persistent allocations comes the problem of how to inform the network of channel quality. In LTE it has been agreed that an eNB can at any time request a UE to send an aperiodic CQI report by sending it an uplink grant with an aperiodic CQI trigger flag set to “on”. The latest agreement in 3GPP is not to support periodic CQI transmission on the PUSCH. However, the inventors have determined that PUSCH-based reporting formats could potentially provide gains in persistent/semi-persistent allocation scenarios, because transmission of UL grants for the sole purpose of triggering an aperiodic CQI reports becomes costly in term of PDCCH resource consumption.
It was agreed in the RAN WG1 meeting 52bis in Shenzhen, China to not include periodic CQI reporting on the PUSCH into the LTE specification, and in fact aperiodic reports can anyway be triggered periodically by the eNB. However, with persistent/semi-persistent allocations there can be potential issues, since when there is a large number of users, triggering aperiodic CQI reports with a UL grant becomes very inefficient. This is exactly the situation that would exist when there is a need for many persistent allocations. One possibility would be to utilize the PUCCH based CQI formats. However they are not able to deliver detailed frequency information to assist the eNB in the scheduling decision due to the low number of payload bits. Moreover, the DRX pattern might limit the possibilities to send PUCCH based CQI for users concentrated for VoIP. Hence there is clearly a need for a mechanism to be able to efficiently get detailed CQI information with the (semi) persistent transmissions.